Control fault veto



Nov. 23, 1965 G. s. BISHOP 3,218,938

CONTROL FAULT VETO Original Filed Dec. 26, 1963 United States Patent M 3,218,938 CONTROL FAULT VE'IO Geoffrey S. Bishop, London, England, assignor to Elliott Brothers (London) Limited, London, England, a British company Orig'nal application Dec. 26, 1963, Ser. No. 333,528. Divided and this application Aug. 10, 1964, Ser. No. 389,304

Claims priority, application Great Britain, Jan. 4, 1963, 583/63 Claims. (Cl. 91-448) This application is a division of patent application Serial No. 333,528, filed December 26, 1963.

This invention relates to hydraulic actuators, and more particularly to a hydraulic actuator having incorporated therein a veto valve which can override the action of the normal control valve of the actuator.

An actuator according to the invention may be used in a control fault veto system for aircraft of the kind described and claimed in my co-pending United States patent application Serial No. 333,528. The actuator according to the present invention has utility apart from the abovementioned control fault veto system and may be used for any purpose where it is desired to provide an actuator having a separate overriding control.

One object of the invention is to provide a hydraulic actuator having a veto valve incorporated therein which is able to override the action of the control valve without interfering with its position.

Another object is to provide a hyd aulic actuator containing a veto valve which in one position allows the actuator to function normally under; the control of the control valve and having operative positions in which the actuator piston is allowed to move freely in one or other of its direction under the normal control of the control valve but is prevented from being moved in the opposite direction.

A further object is to provide an improved hydraulic actuator containing an override control.

As broadly claimed, the invention embraces a hydraulic actuator having a double-acting piston and cylinder which is controlled by a control valve in the usual way, which control valve controls the admission and release of fluid to or from the two ends of the cylinder so that the piston is caused to move under the control of the control valve, and having incorporated therein a veto valve which controls the supply of the hydraulic medium to the control valve so that the veto valve is able to exercise an overriding control without interfering with the actuation of the control valve. Preferably the veto valve is arranged to have a neutral position in which the piston is allowed to operate normally under the control of the control valve and two opposite operative positions in one of which the piston is allowed to move freely in one direction under the control of the control valve and in the other of which the piston is allowed to move freely in the said other direction under the control of the control valve but is in either case prevented from being actuated in the opposite direction.

In one form of actuator according to the invention the control valve is a spool valve operating in a ported control valve cylinder and having two cylindrical end portions separated by a stem to control the passage of hydraulic fluid into and out of the two ends of the cylinder and a third cylindrical portion between the said two cylindrical end portions, the veto valve is a spool valve operating in a ported veto valve cylinder and having two cylindrical portions separated by a stern, and the actuator comprises two passages leading from the veto valvecylinder at points between the veto valve cylindrical portions into the control valve cylinder at points respectively between the cylindrical end portions and the central cylindrical por- 3,218,938 Patented Nov. 23, 1965 ICE tion of the control valve, and a high pressure fluid supply duct leading into the veto valve cylinder between the cylindrical portions of the veto valve, whereby a movement of the veto valve in either direction to close one of the two passages prevents the supply of fluid to the cylinder in response to a movement of the control valve in the opposite direction.

In another form of actuator according to the invention, the piston is provided with a piston rod having substantially one-half the cross-sectional area of the piston, the piston rod passing through one end of the cylinder, and the actautor comprises a high pressure fluid supply duct, a permanent connection between the fluid supply duct and the said one end of the cylinder, the control valve being a spool valve in a control valve cylinder and having three cylindrical portions separated by stem portions, the central cylindrical portion normally closing a port leading to the other end of the cylinder, the veto valve being a spool valve in a veto valve cylinder and having three cylindrical portions separated by stem portions, and the actautor comprises passages leading respectively from points in the veto valve cylinder between the cylindrical end portions and the central cylindrical portion of the veto valve into the corresponding points in the control valve cylinder between the cylindrical end portions and the central cylindrical portion of the control valve, a further duct leading from the high pressure fluid supply duct to the veto valve cylinder at a point between one cylindrical end portion and the central cylindrical portion of the veto valve, another duct leading from the veto valve cylinder at a point between the other cylindricalend portion and the central cylindrical portion of the veto valve to a low pressure exhaust passage, whereby movement of the veto valve in either direction to close one of the passages prevents the supply of fluid to the cylinder in response to a movement of the control valve in the same direction.

To promote a ready understanding of the invention and its mode of operation two embodiments of the invention will now be described with reference to the accompanying drawings in which:

FIGURE 1 is a diagrammatic section of a known type of hydraulic actuator controlled by a known type of four-port valve;

FIGURE 2 is a diagrammatic section of an actuator similar to that of FIGURE 1 incorporating a veto valve;

FIGURE 3 is a diagrammatic section of another type of known hydraulic actuator including a known type of three-port control valve; and

FIGURE 4 is a diagrammatic section of the valve of FIGURE 3 incorporating a veto valve.

Like reference numerals are used for like parts in all the figures.

Referring now to FIGURE 1, the hydraulic actuator shown therein comprises a casing 11 formed with a fluid pressure cylinder 12 containing a piston 13 connected to a piston rod or ram 14, which projects from one end of the cylinder 12, it being understood that an appropriate fluid pressure seal or gland is provided at the point at which the piston 14 emerges through the end of the casing 11. Lying parallel to the cylinder 12 is a valve cylinder 15 containing a spool valve having two lands 16 and 17 connected by an operating rod 18 which passes through the side of the casing 11 there being again an appropriate fluid seal or gland. The spacing of the two lands 16 and 17 is such that when the spool valve is in a central or new tral position the lands 16 and 17 respectively close two passages 19 and 20 connected to the two ends of the cylinder 12. The two ends of the valve cylinder 15 are connected to the low pressure or exhaust side of the hydraulic system by two passages, respectively 21 and 22,

which join together in a common low pressure outlet 23. A high pressure inlet 24 connects with a passage which opens into the central portion of the cylinder between the two lands 16 and 17 of the spool valve.

With the parts in the positions shown in FIGURE 1 the actuator is in a neutral position and the fluid pressure applied through the inlet 24 acts on the inner faces of the lands 16 and 17 so that the forces exerted on the rod 18 are balanced. Similarly, the forces acting on the two faces of the piston 13 due to fluid pressure previously applied are balanced and the piston rod 14 is stationary. If the rod 18 is moved to the left in FIGURE 1 fluid under pressure is admitted through the passage 19 to the lefthand end of the cylinder 12, and at the same time the passage 20 is opened to the same extent to the passage 22 and thence to the low pressure outlet 23. In consequence the piston 13 and the piston rod 14 are moved to the right and they will continue to move until either the piston has reached the maximum limit of its stroke or until the rod 18 is moved back to its original position. If, on the other hand, the rod 18 is moved to the right in FIGURE 1 then fluid under pressure from the inlet 24 is admitted through the passage 20 to the right-hand end of the cylinder 12 while the left-hand end is connected through the passage 19 which is opened to exactly the same extent via the passage 21 to the low pressure outlet 23, and the reverse action takes place, that is to say, the piston 13 and piston rod 14 are moved to the left until either these members have moved to the maximum permitted extent or the rod 18 is returned to its initial position. This type of valve is known but a full description has been given so that the functioning of the novel actuator shown in FIGURE 2 may more readily be understood.

In the actuator of FIGURE 2 the casing 25 is of somewhat different form but it contains a cylinder 12 identical with the cylinder 12 of FIGURE 1 and an identical piston 13 and piston rod or ram 14. The control valve connected to the rod 18 and operating in the valve cylinder 29 is somewhat different in that it is provided with three lands, respectively 26, 27 and 28. The two lands 26 and 28, when in the central position, cover the two passages 19 and 20 leading from the two ends of the cylinder 12. Both ends of the cylinder 29 are connected respectively through passages 30 and 31 to an exhaust or low pressure putlet passage which terminates in a low pressure out- Between the lands 26 and 27 is a passage 33 leading to a veto valve cylinder 34 and between the lands 27 and 28 is still another passage 35, also leading to the cylinder 34. Both the passages 33 and 35 lead into the cylinder 34 between two lands, respectively 36 and 37, of a veto valve control rod 38 extending through the casing. The centre of the cylinder 34 is provided with another passage 39 which is the high pressure inlet passage. The two ends of the cylinder 34 are connected respectively by passages 40 and 41 to the low pressure outlet passage 32.

With the parts in the positions shown in FIGURE 2, operation of the control valve by means of the rod 18 causes the actuator to function normally. For example, if the valve is moved to the left in FIGURE 2 then the land 26 uncovers the passage 19 which is connected through the passage 32 and the cylinder 34 to the high pressure inlet 39, and the same movement uncovers the passage 20 to the same extent and connects this passage to the low pressure exhaust outlet 32. On the other hand, movement of the spool valve to the right by means of the rod 18 causes the passage 20 to be uncovered and connected through the passage 35 and the cylinder 34 to the high pressure inlet 39 and at the same time causes the land 26 to uncover an equal amount of the passage 19 to connect the passage 19 to the low pressure outlet 32. If, by operation of the rod 38, the veto valve is moved to the right in FIGURE 2, to the appropriate extent, the passage 33 is closed and this alters the operation of the actuator.

If, with the passage 33 closed, the control valve is movedto the left, the passage 19 is uncovered and is thus open to a part of the cylinder 29 and to the passage 33, but since the latter passage is closed high pressure fluid cannot flow into the left-hand end of the cylinder 12, and although the movement of the control valve also causes the passage 20 to be opened and connected through the passage 31 to the low pressure outlet passage 32, no movement of the piston 13 takes place because the control exercised by means of the rod 18 has been vetoed by the movement of the veto valve by means of the rod 38. If, with the veto valve in the same position, i.e. with the passage 33 closed, the control valve is moved to the right by operation of the rod 18, high pressure fluid entering through the inlet passage 39 passes through the centre portion of the cylinder 34, through the passage 35, through a part of the cylinder 29 and through the passage 20 into the right-hand end of the cylinder 12, and fluid at low pressure is exhausted through the passage 19 and the lefthand end of the cylinder 29 and the passages 30 and 41 to the low pressure outlet 32. Thus movement of the control rod 38 of the veto valve to the right allows the piston 13 to move to the left under the control of the control valve, but prevents movement of the piston 13 to the right.

If, now, the control rod 38 is moved to the left, so that the passage 35 is closed, the opposite conditions prevail. Under these conditions movement of the control rod 18 of the control valve to the right produces no result, since high pressure fluid is unable to flow into the passage 39 to gain access to the passage 20. On the other hand, movement of the control rod 18 to the left allows the actuator to function normally. Thus, a control device coupled to the control rod 38 of the veto valve can either leave the actuator free to move in either direction as directed by the control rod 18, or it can veto the commands applied to the control rod 18 in one direction or the other.

In FIGURE 2, two dimensions marked 6 will be observed. These represent the distance which the veto valve must move before the veto action is completed in one direction or the other. They will be referred to again at a later stage.

FIGURE 3 shows a conventional type of actuator having a three port control valve. It comprises a casing 42 containing a cylinder 43. A piston 44 has attached to it a piston rod 45 having a cross-sectional area of one half that of the piston 44. A control valve cylinder 46 contains a spool valve having two lands 47 and 48 connected to each other and to a control rod 49 which extends outwardly through the casing 42. In the normal equilibrium position the land 47 covers a passage 50 which leads from the cylinder 46 to the end of the cylinder 43 opposite that through which the piston rod projects. The other end of the cylinder 43 is permanently connected by a passage 51 to a high pressure inlet passage 52. The land 48 of the control valve merely functions as a guide in the cylinder 46. The two ends of the cylinder 46 are connected respectively by passages 53 and 54 to a low pressure outlet passage 55.

The operation of this actuator is as follows. If the spool valve is moved to the left in FIGURE 3, by operation of the control rod 49, high pressure fluid flows through the inlet passage 52 and the passage 50 into the left-hand end of the cylinder 43. By virtue of the fact that the whole face of the piston 44 is acted upon by the high pressure fluid in the one direction whereas, due to the large piston rod, only one half the area of the piston is acted upon in the other direction the piston 44 moves to the right, expelling fluid through the passage 51 back to the high pressure inlet, and this movement continues until either the piston 44 has moved to its extreme limit or the control valve is moved back to its neutral position by means of the control rod 49. If, on the other hand, the control rod 49 is moved to the right, then the left-hand end of the cylinder 43 is connected through the passage 4 t0 the Q pressure outlet 55 and high pressure fluid enters the right-hand end of the cylinder 43 through the inlet 52 and the passage 51. The piston 44 and the piston rod 45 accordingly move to the left until they have reached the end of their stroke or the control valve is closed again.

FIGURE 4 shows a three port type of actuator with the addition of a veto valve according to the invention. The casing 56 contains the cylinder 43, the piston 44 and its attendant piston rod 45, as in FIGURE 3, but it contains two spool valves. The lower spool valve operating in cylinder 57, which is the control valve, has three lands respectively 58, 59 and 60. When in the central or neutral position the land 59 covers a passage 61 leading from the closed end of the cylinder 43. The other end of the cylinder 43 is permanently connected through the passage 62 to a high pressure inlet passage 63. The control valve has a control rod 64.

Between the lands 58 and 59 a passage 65 leads from the control valve cylinder 57 to a veto valve cylinder 66 and between the lands 59 and 60 a further passage 67 also leads into the veto valve cylinder 66. The veto valve cylinder 66 contains a veto valve composed of three lands, respectively 68, 69 and 70, joined together and connected to a control rod 71. The two portions of the cylinder 66 into which the passages 65 and 67 open are separated by the central land 69. Between the lands 68 and 69 a further passage 72 leads from the cylinder 66 into a low pressure outlet passage 73. The two ends of the cylinder 57 are also connected by means of passages 74 and 75 to the low pressure outlet 73 and the two ends of the cylinder 66 are connected to the low pressure outlet 73 by respective passages 76 and 77. Between the lands 69 and 70 a passage 78 leads from the cylinder 66 to a high pressure inlet 63.

In operation, with the veto valve in the position shown, the piston 44 and piston rod 45 may be moved in either direction under the control of the control rod 64, in th same way that the same parts are moved under the control of the control rod 49 in FIGURE 3. If, now, the control rod 71 is moved to the right in FIGURE 4 until the land 68 covers the passage 65, then movement of the control rod 64 to the right to allow the land 59 to open the passage 61 into the cylinder 43 has no effect, since the fluid in the left-hand end of the cylinder 43 cannot escape into the low pressure outlet 73. On the other hand, movement of the control rod 64 to the left in FIG- URE 4 will cause the piston 44 and piston rod 45 to move to the right since there is a connection from the inlet 63 through the cylinder 66, the passage 67 and the passage 61 into the left-hand end of the cylinder 43. If, on the other hand, the veto valve control rod 71 is moved to the left until the land 70 covers the passage 78 then movement of the control rod 64 to the right allows high pressure fluid to flow from the inlet 63 through the passage 62 and into the right-hand end of the cylinder 43, because low pressure fluid is allowed to escape through the passage 61 and the passages 65 and 72 into the low pressure outlet 73. Movement of the control rod 64 to the left, however, produces no elfect, since high pressure fluid cannot pass from the passage 78 through the passage 67 and into the left-hand end of the cylinder 43.

The clearances marked 5 in the drawings represent a small amount of lost motion in the veto valve, from its neutral position before it becomes eifective. Its provision is, of course, optional. It may be provided where it is desirable that the member connected to the veto valve control rod must move a substantial distance before it interferes with the normal operation of the actuator.

I claim:

1. A hydraulic actuator comprising a double-acting piston and cylinder, a control valve for controlling the admission and release of hydraulic fluid to and from the two ends of said cylinder to control the movement of said piston therein, and a veto valve for controlling the flow of hydraulic fluid through said control valve to exercise an overriding control, said veto valve having a neutral position in which said piston is allowed to operate normally under the control of said control valve, a first operative position in which said piston is allowed to move normally under the control of said control valve in one direction but is prevented from being actuated in the other direction, and a second operative position in which said piston is allowed to move normally under the control of said control valve in said other direction but is prevented from being actuated in said one direction.

2. A hydraulic actuator comprising a double-acting piston and cylinder, a control valve in the form of a spool valve operating in a ported control valve cylinder and having two end lands separated by a stem to control the passage of hydraulic fluid into and out of the two ends of said cylinder and a third land between said two end lands, a veto valve in the form of a spool valve operating in a ported veto valve cylinder and having two lands separated by a stem, two passages leading from said veto valve cylinder at points between the veto valve lands into said control valve cylinder at points respectively between said end lands and said central land of said control valve, and a high pressure fluid supply duct leading into said veto valve cylinder between said lands of said veto valve, whereby a movement of said veto valve in either direction from its central position to close one of said two passages prevents the supply of fluid to said cylinder in response to a movement of said control valve in the opposite direction.

3. A hydraulic actuator as claimed in claim 2 in which the separation between said lands of said veto valve is greater than the separation between said passages, whereby said veto valve is permitted a certain movement in either direction from its central position before it begins to close a passage.

4. A hydraulic actuator comprising a double-acting cylinder and piston, said piston being provided with a piston rod having substantially one-half the cross-sectional area of said piston, said piston rod passing through one end of said cylinder, a high pressure fluid supply duct, a permanent connection between said fluid supply duct and said one end of said cylinder, a control valve in the form of a spool valve in a spool valve cylinder and having three lands separated by stem portions, the central land normally closing a port leading to the other end of said cylinder, a veto valve in the form of a spool valve in a veto valve cylinder and having three lands separated by stem portions, passages leading respectively from points in said veto valve cylinder between the end lands and said central land of said veto valve into the corresponding points in said control valve cylinder between the end lands and said central land of said control valve, a further duct leading from said high pressure fluid supply duct to said veto valve cylinder at a point between one end land and said central land of said veto valve, another duct leading from said veto valve cylinder at a point between the other end land and said central land of the veto valve to a low pressure exhaust duct, whereby movement of the veto valve in either direction to close one of the passages prevents the supply of fluid to said cylinder in response to a movement of the control valve in the same direction.

5. An actuator as claimed in claim 4 in which the separation of the end lands of said veto valve is greater than the separation between said passages, whereby said veto valve is permitted a certain movement in either direction from its central position before it begins to close a passage.

References Cited by the Examiner UNITED STATES PATENTS 2,179,179 11/1939 Fischel 9l448 2,194,078 3/ 1940 Simonds 9l448 3,001,511 10/ 1961 Poyner 9l448 SAMUEL LEVINE, Primary Examiner. FRED E. ENGELTHALER, Examiner. 

1. A HYDRAULIC ACTUATOR COMPRISING A DOUBLE-ACTING PISTON AND CYLINDER, A CONTROL VALVE FOR CONTROLLING THE ADMISSION AND RELEASE OF HYDRAULIC FLUID TO AND FROM THE TWO ENDS OF SAID CYLINDER TO CONTROL THE MOVEMENT OF SAID PISTON THEREIN, AND A VETO VALVE FOR CONTROLLING THE FLOW OF HYDRAULIC FLUID THROUGH SAID CONTROL VALVE TO EXERCISE AN OVERRIDING CONTROL, SAID VETO VALVE HAVING A NEUTRAL POSITION IN WHICH SAID PISTON IS ALLOWED TO OPERATE NORMALLY UNDER THE CONTROL OF SAID CONTROL VALVE, A FIRST OPERATIVE POSITION IN WHICH SAID PISTON IS ALLOWED TO MOVE NORMALY UNDER THE CONTROL OF SAID CONTROL VALVE IN ONE DIRECTION BUT IS PREVENTED FROM BEING ACTUATED IN THE 